[FFmpeg-trac] #9085(avcodec:reopened): JPEG: YCCK too green

FFmpeg trac at avcodec.org
Wed Mar 24 00:18:00 EET 2021

#9085: JPEG: YCCK too green
             Reporter:  Balling     |                    Owner:
                 Type:  defect      |                   Status:  reopened
             Priority:  normal      |                Component:  avcodec
              Version:  git-master  |               Resolution:
             Keywords:  mjpeg cmyk  |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |

Comment (by Balling):

 Okay my latest idea is that it is subsampling issue, subsampled CMYK and
 YCCK (yeah, CMYK is also insanely affected, at least that uses in Ci
 endcoding, see #4772) are good and not subsampled are bad. That is
 regression of d56c373391d334d3dc29c752955fd17f0cef7ff9.

 Franky speaking I am starting to fear that this is just a problem of not
 limiting CMYK green values... CMYK is not a triange or prism (in XYZ) and
 so we get that problem. Green should be limited to much lower values.

 I also found good test here: https://github.com/mozilla/mozjpeg/issues/23

 Also, we will try to fix this in Chromium, and if it will work with our
 native jpeg decoder, we will try to get to fallback (that is ffmpeg).

Ticket URL: <https://trac.ffmpeg.org/ticket/9085#comment:23>
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